Two effectors

• Knocked out independently
• Host chlorosis measured

Communication

• Stories told through figures

Scales matter

• Indication of quantities

Context matters

• Figures are what you remember of a story

Binary thinking

• The same or not the same
• Larger or smaller
• What about uncertainty?

Four effectors

• Bacterial effectors
• Inoculate wild-type plants
• Measure growth (CFU)

Four bar plots

• Do the effectors have the same effect?

Add error bars

• Do the effectors have the same effect?

Error bars

• Estimates of uncertainty
• But uncertainty of what?
• standard deviation (sd):
  • describes the data: how much members of the group differ from the mean
• standard error (of the mean) (sem):
  • describes the estimate of the mean: standard deviation of the estimate of the mean

SD or SEM?

• Which was used (& which would you want to know)?

Raw data

• Are they the same responses?

What does mean mean?

• Does having the same mean imply having the same response?

What does mean mean?

• Unequal sample sizes

What does mean mean?

• Outliers

What does mean mean?

• Bimodal distribution

We use figures as guides…

• “Figures tell a story, but we actually only believe the stats”
• P<0.05, t-test (NHST), a description if you’re lucky
• Do the distributions support use of NHST or t-test (are the data Normal)?

…we trust the P-values

• Bar plots hide inappropriate assumptions

Source: Weissgerber et al. (2015)

Figures can mislead

• reinforce poor practice
  • binary thinking
  • overlooking data distributions and wrong statistical assumptions for tests
  • overlooking uncertainty
• suggest neat stories (P<0.05)
  • data, like life, can be messy

Now what?

• “Thanks for undermining me. Now what do I do about it?”
• Other data representations are available
• Data visualisation/statistics training courses
  • Research Data Visualisation Workshops
  • Data Carpentry
  • Software Carpentry

Anscombe’s Quartet

• Four datasets: same means and standard deviations

Boxplots

• Median, interquartiles, outliers

Raw data

• 1D scatterplots

Box and raw data

• Boxplots and jittered 1D scatterplots

Violin plot

• Data density estimate

Violin and raw data

• Stacked, not jittered, data